1. Field of the Invention
The present invention relates to an X-ray computed tomography scanner for performing helical scanning.
2. Description of the Related Art
A function of setting a scanning range using a scanogram (X-ray transmission image) is known as one of functions of an X-ray computed tomography scanner (referred to as an X-ray CT scanner hereinafter) (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 9-164135). This function is performed to set a range designated freely by a user on a scanogram as a scanning range. Using this function, the user can determine a scanning range visually and simply.
The scanning range set by the above function is a range within which an image should be captured by image reconstruction. In helical scanning, in order to capture an image in a certain position, the image needs to be interpolated by data before and after the position. Data is therefore collected from a range that is larger than the scanning range described above. In other words, the range of application of X-rays to a subject becomes larger than the above scanning range.
It is feared that a user who does not understand the above characteristic of the helical scanning will set a scanning range without considering that X-rays are applied outside a designated range.